The correct answer to this open question is the following.
Piaget's theory of cognitive development places the case of Thomas in the Formal Operation Stage, 12 years-old and up. In this state, Jean Piaget established that people are in a period of experimenting and learning. Swiss sociology Jean Piaget says that during this period, people experiment and learn through interacting with other people and different environments.
Kohlberg's theory of morality places Thomas in level 3 of his Theory: Postconventional Morality. Here, the author says that people understand the rules of morality and their consequences, including the respect for the dignity of all humans. It is an important ethic principle.
Erikson's theory of identity formation places Thomas on stage 5, Identity vs. Confusión. Here, the teenager is asking the question "who am I?" and tries to find a place in social groups.
Taking those theories into consideration it is understandable that Sixteen-year-old Thomas is in a difficult position. Trying to break into the popular group at school and he has been invited to a party on Saturday in one of the group's members' house.
Although he wants to go, he has some issues to resolve first because he has already volunteered to help his church youth group with an activity for first graders that night. In addition, he knows that there will be drinking at the party, and he has promised his mother that he would never drink in high school, and she trusts him.
After considering those above-mentioned theories, Thomas would spend a difficult time making a decision because he is confronted with his absolute desire to go to the party and be considered a member of that group, against the moral decision of promising his mother not to drink, plus his commitment to go do volunteering work.
Knowing that he is 16 and really wants to experiment and being recognized, he will attend the party, he will drink to be accepted, and he later will have to face the consequences.